Cooling system

ABSTRACT

The present invention provides a cooling system ( 1 ), comprising a receiver tank ( 2 ), an evaporator ( 3 ), a compressor ( 4 ) and a gas cooler ( 5 ), wherein the receiver tank ( 2 ) comprises a fluid inlet ( 6 ), a liquid outlet ( 7 ) and a gas outlet ( 8 ); the evaporator ( 3 ) comprises an evaporator inlet ( 9 ) and an evaporator outlet ( 10 ), the compressor ( 4 ) comprises a compressor inlet ( 11 ) and a compressor outlet ( 12 ); the gas cooler ( 5 ) comprises a cooler inlet ( 13 ) and a cooler outlet ( 14 ); and the liquid outlet ( 7 ) of the receiver tank ( 2 ) is connected to the evaporator inlet ( 9 ) via a first conduit ( 15 ), the evaporator outlet ( 10 ) is connected to the compressor inlet ( 11 ) via a second conduit ( 16 ), the compressor outlet ( 12 ) is connected to the cooler inlet ( 13 ) via a third conduit ( 17 ), and the cooler outlet ( 14 ) is connected to the fluid inlet ( 6 ) of the receiver via a fourth conduit ( 18 ), wherein at least one of the first conduit ( 15 ) and the fourth conduit ( 18 ) comprises a pressure regulator ( 19,25 ), and the gas outlet ( 8 ) of the receiver tank is connected to the evaporator inlet ( 9 ) via a fifth conduit ( 20 ) and a gas flow regulator ( 21,22 ), such that a flow of liquid refrigerant in the first conduit ( 15 ) may be controlled by operating the gas flow regulator ( 21,22 ) during use.

FIELD OF THE INVENTION

The present invention relates to cooling systems, more particularlydirect expansion cooling systems for CO2-refrigerant media.

BACKGROUND

Direct expansion (DX) cooling systems are a common refrigeration systemusing the vapor-compression refrigeration cycle.

A typical prior art DX cooling system is shown in FIG. 1. In the DXcooling system, the pressure and temperature of the liquid refrigerantprovided to an evaporator 3 is commonly controlled by use of anexpansion valve 25, e.g. a modulating control valve or pressureregulator, arranged between a receiver tank 2 and the evaporator 3. Anadditional expansion valve 19 is required between a gas cooler 5 and thereceiver tank 2 when the refrigerant is transcritical exiting the gascooler 5, such that subcritical conditions are ensured in the receivertank 2 to allow separation of the refrigerant into a gas and a liquidphase. In a transcritical DX cooling system the refrigerant is atsubcritical conditions when exiting the expansion valve 19 arrangedbetween the receiver and the gas cooler and at transcritical conditionswhen exiting the compressor 4. In a subcritical DX cooling system, therefrigerant is at subcritical conditions throughout the system, and theexpansion valve 19 arranged before the receiver tank 2 is not required.

Commonly, the capacity of the evaporator 3 is controlled by regulatingthe effect of the compressor 4 and the expansion valve 19 arrangedbetween the gas cooler 5 and the receiver tank 2.

Prior art DX cooling systems have various disadvantages with regards tothe control of the cooling capacity, in particular when lower coolingcapacities are required.

The aim of the present invention is to provide a DX cooling system whichalleviates or removes at least some of the disadvantages of the priorart cooling systems. More particularly, the present invention provides aDX cooling system having an improved control of the cooling capacity, animproved energy efficiency as well as an improved utilization of theevaporator.

SUMMARY OF THE INVENTION

The present invention is defined by the attached claims and in thefollowing:

In a first aspect, the present invention provides a cooling systemcomprising a receiver tank, an evaporator, a compressor and a gascooler, wherein

-   -   the receiver tank comprises a fluid inlet, a liquid outlet and a        gas outlet;    -   the evaporator comprises an evaporator inlet and an evaporator        outlet,    -   the compressor comprises a compressor inlet and a compressor        outlet;    -   the gas cooler comprises a cooler inlet and a cooler outlet; and    -   the liquid outlet of the receiver tank is connected to the        evaporator inlet via a first conduit, the evaporator outlet is        connected to the compressor inlet via a second conduit, the        compressor outlet is connected to the cooler inlet via a third        conduit, and the cooler outlet is connected to the fluid inlet        of the receiver tank via a fourth conduit, wherein    -   at least one of the first conduit and the fourth conduit        comprises a pressure regulator, and    -   the gas outlet of the receiver tank is connected to the        evaporator inlet via a fifth conduit and a gas flow regulator,        such that a flow of liquid refrigerant in the first conduit may        be controlled by operating the gas flow regulator during use.        That is, the flow of liquid refrigerant entering the evaporator        inlet via the first conduit may be controlled by operating the        gas flow regulator during use

In other words, the gas outlet of the receiver tank is connected to theevaporator inlet via the fifth conduit and the gas flow regulator, suchthat a flow of gaseous refrigerant from the receiver tank may enter theevaporator during use.

The cooling system may be operated as a transcritical cooling system ora subcritical cooling system. In a transcritical cooling system, thepressure and temperature conditions are arranged such that a refrigerantwill be transcritical in the gas cooler and subcritical in the receivertank. In a subcritical cooling system, the refrigerant will besubcritical throughout the cooling system. In a subcritical coolingsystem, the gas cooler may also be termed a gas condenser.

The gas flow regulator may be defined as a modulating gas control valve.The pressure regulator may be a modulating fluid control valve. In atranscritical cooling system, the pressure regulator may also be termeda modulating high-pressure control valve.

In an embodiment, the cooler outlet is connected to the fluid inlet ofthe receiver tank via a fourth conduit and a pressure regulator.

In an embodiment of the cooling system, the gas flow regulator isarranged such that a lowering of a flow of gaseous refrigerant in thefifth conduit by operating the gas flow regulator will increase the flowof liquid refrigerant in the first conduit. In other words, a loweringof a flow of gaseous refrigerant in the fifth conduit by operating thegas flow regulator will increase the pressure in the receiver tank andthus increase the flow of liquid refrigerant in the first conduit.

In an embodiment of the cooling system, the gas outlet of the receivertank is connected to the evaporator inlet via the fifth conduit and thegas flow regulator, such that a mixture of gaseous refrigerant from thefifth conduit and liquid refrigerant from the first conduit may enterthe evaporator inlet during use.

In an embodiment of the cooling system, the fifth conduit comprises afirst end connected to the gas outlet of the receiver tank and a secondend connected to the first conduit, such that gaseous refrigerant fromthe gas outlet of the receiver tank may be mixed with a liquidrefrigerant from the liquid outlet of the receiver tank before enteringthe evaporator inlet during use.

In an embodiment of the cooling system, the liquid outlet of thereceiver tank is arranged such that an increased pressure of gaseousrefrigerant in the receiver tank will force liquid out of the receivertank via the liquid outlet during use.

In an embodiment of the cooling system, the first conduit and the fifthconduit are connected to the evaporator inlet via a sixth conduit.

In an embodiment of the cooling system, the fifth conduit is connectedto the evaporator inlet via the first conduit.

In an embodiment of the cooling system, the sixth conduit has an innercross-sectional area larger than the cross-sectional area of the firstconduit.

In an embodiment of the cooling system, the gas flow regulator is atwo-way valve. The two-way valve may be a modulating control valve.

In an embodiment of the cooling system, the two-way valve is arrangedin, or constitutes a part of, the fifth conduit.

In an embodiment of the cooling system, the first conduit, the fifthconduit and the sixth conduit is interconnected by a three-way couplingfeaturing a first inlet connected to the fifth conduit, a second inletconnected to the first conduit and an outlet connected to the evaporatorinlet or the sixth conduit, wherein the second inlet is arranged at anangle relative to the outlet, such that an ejector effect of a gaseousrefrigerant flow from the fifth conduit acting on a liquid refrigerantin the first conduit is minimized during use. The angle may be about90°.

In an embodiment of the cooling system, the gas flow regulator is athree-way valve. The three-way valve may be a modulating control valve.

In an embodiment of the cooling system, the three-way valve comprises afirst inlet connected to the first conduit, a second inlet connected tothe fifth conduit and an outlet connected to the evaporator inlet or thesixth conduit.

In an embodiment, the cooling system comprises a first pressure sensorand a first temperature sensor, arranged in the second conduit, and asecond pressure sensor and a second temperature sensor arranged in thefourth conduit. The second pressure sensor and the second temperaturesensor may be arranged in the fourth conduit upstream a pressureregulator in the fourth conduit.

In an embodiment of the cooling system, the second pressure sensor andthe second temperature sensor may be replaced by a pressure transmitter.In embodiments featuring a pressure transmitter, the cooling system maybe a subcritical cooling system. The pressure transmitter may beconnected to any of a gas cooler/condenser fan or a gas cooler/condenserpump.

In a second aspect, the present invention provides a method ofcontrolling a cooling system, wherein the cooling system comprises areceiver tank, an evaporator, a compressor and a gas cooler, wherein

-   -   the receiver tank comprises a fluid inlet, a liquid outlet and a        gas outlet;    -   the evaporator comprises an evaporator inlet and an evaporator        outlet,    -   the compressor comprises a compressor inlet and a compressor        outlet;    -   the gas cooler comprises a cooler inlet and a cooler outlet; and    -   the liquid outlet of the receiver tank is connected to the        evaporator inlet via a first conduit, the evaporator outlet is        connected to the compressor inlet via a second conduit, the        compressor outlet is connected to the cooler inlet via a third        conduit, and the cooler outlet is connected to the fluid inlet        of the receiver via a fourth conduit, wherein    -   at least one of the first conduit and the fourth conduit        comprises a pressure regulator, and    -   the gas outlet of the receiver tank is connected to the        evaporator inlet via a fifth conduit and a gas flow regulator,        and the method comprises the step of:        -   increasing a flow of gaseous refrigerant in the fifth            conduit by controlling the gas flow regulator to obtain a            reduced flow of liquid refrigerant in the first conduit and            a reduced cooling capacity in the evaporator (3); or        -   reducing a flow of gaseous refrigerant in the fifth conduit            (20) by controlling the gas flow regulator (21,22) to obtain            an increased flow of liquid refrigerant in the first conduit            (15) and an increased cooling capacity in the evaporator            (3).

The step of increasing the flow of gaseous refrigerant provides areduced flow of liquid refrigerant in the first conduit by lowering thepressure of the gaseous refrigerant in the receiver tank.

The step of reducing the flow of gaseous refrigerant provides anincreased flow of liquid refrigerant in the first conduit by raising thepressure of the gaseous refrigerant in the receiver tank.

The method of the second aspect may also be termed a method ofregulating the cooling capacity of a cooling system.

In an embodiment of the method according to the second aspect, thefourth conduit comprises a pressure regulator and the step of increasingthe flow of gaseous refrigerant comprises a step of controlling thepressure regulator to decrease the pressure fall between the cooleroutlet and the fluid inlet of the receiver tank. In other words, thestep of increasing the flow of gaseous refrigerant comprises controllingthe pressure regulator to increase the flow of refrigerant from the gascooler to the receiver tank.

In an embodiment of the method according to the second aspect, the firstconduit comprises a pressure regulator and the step of increasing theflow of gaseous refrigerant comprises controlling the pressure regulatorto increase the pressure fall over the first conduit.

In an embodiment, the method according to the second aspect comprises aninitial step of:

-   -   measuring the refrigerant temperature in the second conduit to        obtain a differential temperature curve relative to the boiling        temperature of the liquid refrigerant within the evaporator; and        increasing or reducing a flow of gaseous refrigerant in the        fifth conduit depending on whether the differential temperature        curve shows a falling or rising differential temperature,        respectively.

In a third aspect, the present invention provides a method ofcontrolling a transcritical cooling system, wherein the cooling systemcomprises a receiver tank, an evaporator, a compressor and a gas cooler,wherein

the receiver tank comprises a fluid inlet, a liquid outlet and a gasoutlet;the evaporator comprises an evaporator inlet and an evaporator outlet,the compressor comprises a compressor inlet and a compressor outlet;the gas cooler comprises a cooler inlet and a cooler outlet; andthe liquid outlet of the receiver tank is connected to the evaporatorinlet via a first conduit, the evaporator outlet is connected to thecompressor inlet via a second conduit, the compressor outlet isconnected to the cooler inlet via a third conduit, and the cooler outletis connected to the fluid inlet of the receiver via a fourth conduit anda pressure regulator, whereinthe gas outlet of the receiver tank is connected to the evaporator inletvia a fifth conduit and a gas flow regulator, and the method comprisingthe step of:

-   -   increasing a flow of gaseous refrigerant in the fifth conduit by        controlling the pressure regulator to decrease the pressure fall        between the cooler outlet and the fluid inlet of the receiver        tank; or    -   reducing a flow of gaseous refrigerant in the fifth conduit (20)        by controlling the pressure regulator to increase the pressure        fall between the cooler outlet and the fluid inlet of the        receiver tank.

In other words, by controlling the pressure regulator to decrease orincrease the pressure fall between the cooler outlet and the fluid inletof the receiver tank, the flow of refrigerant to the receiver tank isincreased or decreased, and the pressure in the gaseous refrigerant inthe receiver tank is increased or decreased, respectively.

The cooling system of the methods according to the second and thirdaspect may comprise any of the features of the cooling system accordingto the first aspect.

In an embodiment of any of the aspects of the invention, the coolingsystem is a direct expansion cooling system, preferably for directexpansion of CO₂ as refrigerant. When CO₂ is used as refrigerant, thecooling system operates at transcritical conditions and the fourthconduit comprises a pressure regulator.

The term “evaporator inlet” is intended to mean an inlet through which arefrigerant must pass to enter a heat-transfer area of an evaporator.The evaporator inlet may be an internally arranged inlet of anevaporator unit, to which unit the first and second conduit areconnected, or an external inlet to which the sixth conduit is connected.

SHORT DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below by way of exampleonly and with reference to the following drawings:

FIG. 1 is a schematic drawing of a prior art DX cooling system.

FIG. 2 is a schematic drawing of a first exemplary embodiment of acooling system according to the invention.

FIG. 3 is a schematic drawing of a second exemplary embodiment of acooling system according to the invention.

FIG. 4 is a schematic drawing of a third exemplary embodiment of acooling system according to the invention.

FIG. 5 is a schematic drawing of a fourth exemplary embodiment of acooling system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a highly advantageous DX cooling system,wherein the cooling capacity of an evaporator may beregulated/controlled in an improved manner. A particularly preferredrefrigerant for use in the inventive cooling system is CO₂.Corresponding or similar features of the cooling systems shown in FIGS.1-5 are denoted by the same reference numbers.

A first exemplary cooling system according to the invention is shown inFIG. 2. The cooling system features a receiver tank 2, an evaporator 3,a compressor 4 and a gas cooler 5. The receiver tank 2 has a fluid inlet6, a liquid outlet 7 and a gas outlet 8. The evaporator 3 has anevaporator inlet 9 and an evaporator outlet 10. The compressor 4 has acompressor inlet 11 and a compressor outlet 12, and the gas cooler 5 hasa cooler inlet 13 and a cooler outlet 14.

The liquid outlet 7 of the receiver tank 2 is connected to theevaporator inlet 9 via a first conduit 15, the evaporator outlet 10 isconnected to the compressor inlet 11 via a second conduit 16, thecompressor outlet 12 is connected to the cooler inlet 13 via a thirdconduit 17, and the cooler outlet 14 is connected to the fluid inlet 6of the receiver tank via a fourth conduit 18 and a pressure regulator19.

When the cooling system is a transcritical system, a refrigerant of thecooling system will be at transcritical conditions between thecompressor outlet 12 and the pressure regulator 19. The pressureregulator 19 is a modulating control valve arranged to lower thepressure of the transcritical refrigerant flow exiting the gas cooler 5.In this manner, the refrigerant will obtain subcritical conditions andseparate into a gas and a liquid phase in the receiver tank 2. Thecooling system may also be operated under subcritical conditionsthroughout the cooling system. The function of the pressure regulator 19is to optimize the heat removal in the gas cooler in relation to theremaining parts of the cooling system by regulating the high-pressure inthe gas cooler. Further, the pressure regulator 19 ensures that therefrigerant in the receiver tank 2 is subcritical. The receiver tankfunctions as a refrigerant buffer, which is a requirement since theamount of refrigerant in the gas cooler 5 and the evaporator 3 willvary.

The gas outlet 8 of the receiver tank is connected to the evaporatorinlet 9 via a fifth conduit 20 and a two-way gas valve 21 (i.e. a gasflow regulator). In this manner, the pressure in the receiver tank 2,and consequently the flow of liquid refrigerant in the first conduit 15,may be controlled/regulated by operating the two-way gas valve 21.

A significant advantage of using the two-way gas valve 21 to control theflow of liquid refrigerant to the evaporator 2, optionally incombination with controlling the pressure regulator 19, is that thecooling system may operate at a higher evaporation temperature andpressure than in the prior art. In this manner, the suction pressure,i.e. the pressure on the suction side of the compressor, is upheld, andthe high-pressure side, i.e. the section of the cooling system betweenthe compressor outlet and the pressure regulator 19, may have a lowerpressure.

In addition to providing an improved control of the refrigerant flow,the inventive cooling system also ensures an optimal energy efficiencysince the refrigerant gas in the receiver tank 2 is utilized asrefrigerant in the evaporator 3. The gaseous refrigerant provides aminor additional cooling effect, about 2-5%, which is not possible toobtain in the prior art cooling systems.

The turbulence caused by combining the liquid and the gaseousrefrigerant prior to entering the evaporator 3 provides an optimaldistribution of the refrigerant in the evaporator and an optimalutilization of the heat transfer area of the evaporator 3. In particularat lower cooling capacities, i.e. low flow of liquid refrigerant to theevaporator 3, the turbulence provides a significant advantage comparedto the prior art systems. In the prior art systems, the lower coolingcapacity commonly leads to an uneven distribution of the liquidrefrigerant, which in turn lowers the evaporation temperature andpressure. The lowered evaporation temperature may be problematic as itmay cause temperatures at an external side of the evaporator being toolow for its intended use, e.g. goods to be cooled may freeze.

To minimize any ejector-effect the gas flow in the fifth conduit 20 mayhave on the liquid refrigerant in the first conduit 15, the fifth andfirst conduit are connected at an angle α of about 90°. The combinedrefrigerant flow is connected to the evaporator 3 via a common conduit23 (i.e. a sixth conduit). To further optimize the cooling system, thefifth and first conduit 20,15 are connected to a mixing chamber 26 toobtain an optimum mixing of the gaseous and liquid refrigerant beforeentering the evaporator. In the present embodiment, the mixing chamber26 is a three-way pipe connection having a cross-sectional area largerthan a cross-sectional area of the first conduit 15. The differences inthe cross-sectional areas provides a slight pressure drop of the liquidrefrigerant to ensure optimum evaporation conditions in the evaporator.In embodiments not featuring a mixing chamber, the slight pressure dropmay be obtained by ensuring that the cross-sectional area of the commonconduit is larger than the cross-sectional area of the first conduit. Itis noted that it is not essential to have a dedicated arrangement ordevice to obtain the slight pressure drop in the refrigerant before itenters the evaporator. Depending on the operating conditions, the slightpressure drop caused by the flow resistance in the first and/or commonconduit may be sufficient.

In view of the prior art, the cooling system according to the inventionis also more cost-efficient in that an expansion valve arranged betweenthe liquid outlet 7 and the evaporator 3 is not required. Expansionvalves are expensive and constitutes a significant percentage of thetotal system cost.

The condition of the refrigerant in the cooling system is monitored by apressure sensor 27 a and a temperature sensor 28 a arranged close to theevaporator outlet 10, and a pressure sensor 27 b and a temperaturesensor 28 b arranged between the cooler outlet 14 and the pressureregulator 19.

The cooling system may feature a control system which, depending on theinput from the pressure sensors 27 a,b, the temperature sensors 28 a,band any optional external temperature data, may control the pressureregulator 19 and the gas valve 21.

The cooling system may be controlled by measuring the refrigeranttemperature in the second conduit 16 to obtain a differentialtemperature curve relative to the boiling temperature of the liquidrefrigerant within the evaporator 3. Depending on whether thedifferential temperature curve shows a falling or rising differentialtemperature, the flow of gaseous refrigerant in the fifth conduit 15 maybe increased or reduced, and the flow of liquid refrigerant respectivelyreduced or increased, by regulating the two-way gas valve and/or thepressure regulator 19. In prior art DX cooling systems, the flow ofliquid refrigerant is also increased when the differential temperaturecurve increases (i.e. shows an increased overheating of the refrigerant)and decreased when the differential temperature curve decreases, but aflow of gaseous refrigerant entering the evaporator may not becontrolled.

The evaporator 3 may be used to cool any suitable external medium, suchas air or a liquid. Similarly, any suitable external medium may be usedto obtain the required cooling effect in the gas cooler 5.

The operating conditions may vary within a large temperature andpressure range dependent on the type of refrigerant. Suitable operatingconditions will be apparent to the skilled person based on the presentdisclosure.

A second exemplary cooling system according to the invention is shown inFIG. 3. The second exemplary cooling system is substantially similar tothe cooling system in FIG. 2 and provides the same advantages asdescribed above. The second exemplary cooling system features a secondmodulating control valve 25 in the first conduit 15. The second controlvalve is not essential for controlling the cooling system but mayprovide an additional control strategy in that the pressure andtemperature of the liquid refrigerant may be controlled before beingmixed with the gaseous refrigerant from the fifth conduit. Further, thesecond modulating control valve 25 may be used to prevent condensationof refrigerant in the evaporator when the cooling system is shut down.

A third exemplary cooling system according to the invention is shown inFIG. 4. The function of the third exemplary cooling system issubstantially similar to the cooling system in FIG. 3 and provides thesame advantages as described above. However, in the third exemplarycooling system, the two-way gas valve 21 and the second modulatingcontrol valve 25 in FIG. 3, are replaced by a single three-way controlvalve 22.

A fourth exemplary cooling system according to the invention is shown inFIG. 5. Most features of the cooling system are similar to the coolingsystem shown in FIG. 3, except that the pressure regulator 19 has beenremoved and the second pressure sensor and the second temperature sensorare replaced by a pressure transmitter 29. The cooling system is adaptedfor use with a refrigerant having subcritical conditions throughout thecooling system, and the pressure regulator 19 shown in FIGS. 2-4 isconsequently not required to lower the pressure of the refrigerantbefore entering the receiver tank 2. Further, the pressure transmitter29 may be arranged to control a gas cooler (or gas condenser) valve orpump to regulate the cooling capacity of the gas cooler. A requiredpressure drop in the liquid refrigerant may be provided by a modulatingcontrol valve 25 (i.e. a pressure regulator) or any suitable expansionvalve/device. The cooling system may be controlled as described for thecooling systems in FIGS. 2 and 3 by regulating the gas flow in the fifthconduit 20 by use of the two-way gas valve 21, and optionally by use ofthe modulating control valve 25.

1. A cooling system, comprising a receiver tank, an evaporator, acompressor and a gas cooler, wherein the receiver tank comprises a fluidinlet, a liquid outlet and a gas outlet; the evaporator comprises anevaporator inlet and an evaporator outlet, the compressor comprises acompressor inlet and a compressor outlet; the gas cooler comprises acooler inlet and a cooler outlet; and the liquid outlet of the receivertank is connected to the evaporator inlet via a first conduit, theevaporator outlet is connected to the compressor inlet via a secondconduit, the compressor outlet is connected to the cooler inlet via athird conduit, and the cooler outlet is connected to the fluid inlet ofthe receiver via a fourth conduit, wherein at least one of the firstconduit and the fourth conduit comprises a pressure regulator, and thegas outlet of the receiver tank is connected to the evaporator inlet viaa fifth conduit and a gas flow regulator, such that a flow of liquidrefrigerant in the first conduit may be controlled by operating the gasflow regulator during use.
 2. A cooling system according to claim 1,wherein the gas flow regulator is arranged such that a lowering of aflow of gaseous refrigerant in the fifth conduit by operating the gasflow regulator will increase the flow of liquid refrigerant in the firstconduit.
 3. A cooling system according to claim 1, wherein the gasoutlet of the receiver tank is connected to the evaporator inlet via thefifth conduit and the gas flow regulator, such that a mixture of gaseousrefrigerant from the fifth conduit and liquid refrigerant from the firstconduit may enter the evaporator inlet during use.
 4. A cooling systemaccording to claim 1, wherein the fifth conduit comprises a first endconnected to the gas outlet of the receiver and a second end connectedto the first conduit, such that gaseous refrigerant from the gas outletof the receiver may be mixed with a liquid refrigerant from the liquidoutlet of the receiver before entering the evaporator inlet during use.5. A cooling system according to claim 1, wherein the first conduit andthe fifth conduit is connected to the evaporator inlet via a sixthconduit.
 6. A cooling system according to claim 1, wherein the gas flowregulator is a two-way valve.
 7. A cooling system according to claim 1,wherein the first conduit, the fifth conduit and the evaporator inlet isinterconnected by a three-way coupling featuring a first inlet connectedto the fifth conduit, a second inlet connected to the first conduit andan outlet connected to the evaporator inlet, wherein the second inlet isarranged at an angle relative to the outlet, such that an ejector effectof a gaseous refrigerant flow from the fifth conduit acting on a liquidrefrigerant in the first conduit is minimized during use.
 8. A coolingsystem according to claim 9, wherein the angle is about 90°.
 9. Acooling system according to claim 1, wherein the gas flow regulator is athree-way valve.
 10. A cooling system according to claim 9, wherein thethree-way valve comprises a first inlet connected to the first conduit,a second inlet connected to the fifth conduit and an outlet connected tothe evaporator inlet.
 11. A cooling system according to claim 1,comprising a first pressure sensor and a first temperature sensor,arranged in the second conduit, and a second pressure sensor and asecond temperature sensor, or a pressure transmitter, arranged in thefourth conduit upstream a pressure regulator.
 12. A method ofcontrolling a cooling system, wherein the cooling system comprisescomprising a receiver tank, an evaporator, a compressor and a gascooler, wherein the receiver tank comprises a fluid inlet, a liquidoutlet and a gas outlet; the evaporator comprises an evaporator inletand an evaporator outlet, the compressor comprises a compressor inletand a compressor outlet; the gas cooler comprises a cooler inlet and acooler outlet; and the liquid outlet of the receiver tank is connectedto the evaporator inlet via a first conduit, the evaporator outlet isconnected to the compressor inlet via a second conduit, the compressoroutlet is connected to the cooler inlet via a third conduit, and thecooler outlet is connected to the fluid inlet of the receiver via afourth conduit, wherein at least one of the first conduit and the fourthconduit comprises a pressure regulator, and the gas outlet of thereceiver is connected to the evaporator inlet via a fifth conduit and agas flow regulator, and the method comprising the step of: increasing aflow of gaseous refrigerant in the fifth conduit by controlling the gasflow regulator to obtain a reduced flow of liquid refrigerant in thefirst conduit and a reduced cooling capacity in the evaporator; orreducing a flow of gaseous refrigerant in the fifth conduit bycontrolling the gas flow regulator to obtain an increased flow of liquidrefrigerant in the first conduit and an increased cooling capacity inthe evaporator.
 13. A method according to claim 12, wherein the fourthconduit comprises a pressure regulator and the step of increasing theflow of gaseous refrigerant comprises controlling the pressure regulatorto decrease the pressure fall between the cooler outlet and the fluidinlet of the receiver tank.
 14. A method according to claim 12, whereinthe first conduit comprises a pressure regulator and the step ofincreasing the flow of gaseous refrigerant comprises controlling thepressure regulator to increase the pressure fall over the first conduit.15. A method according to claim 12, comprising an initial step of:measuring the refrigerant temperature in the second conduit to obtain adifferential temperature curve relative to the boiling temperature ofthe liquid refrigerant within the evaporator; and increasing or reducinga flow of gaseous refrigerant in the fifth conduit depending on whetherthe differential temperature curve shows a falling or risingdifferential temperature, respectively.